In recent years much has been accomplished in the automation of various bioclinical laboratory procedures. One area in which little progress has been made is in the classification and analysis of cells. The need for the automation of blood cell analysis is manifest. Present day techniques are fragmented, manual (and hence tedious and susceptible to human error), expensive and often inaccurate. They are at best marginally satisfactory in their ability to cope with the large volume demands on the clinical laboratory for blood cell classification.
The analysis of the formed elements (cells and platelets) found in human blood comprises the most common set of laboratory tests required by doctors. These tests are of critical clinical importance both as a screening mechanism and as a means of following the course of a wide variety of diseases, including anemias, infections, heart attacks, damage to body tissues, allergies, etc. Blood tests are also used to monitor the effects of therapeutic agents.
In the case of disorders of the blood and blood forming organs (hematologic diseases), blood analysis is the primary diagnostic tool available to the physician. At present the hematologic diseases, especially leukemia, are poorly characterized and often pose different diagnostic problems, based, in part, on the inadequacy of current manual microscope blood testing methods. The human technoligist, no matter how well trained, can only obtain certain kinds of qualitative information about blood cells by looking at them through a microscope. It is often precisely the variations in the subjective interpretation of this qualitative information (such as the details of the distribution of stained materials in the cell or cell nucleus) that forms the basis of controversy among hematologic experts regarding important diagnostic distinctions as leukemia versus some temporary condition, such as an infection.
A complete blood count (CBC) consists of a red cell (RBC) count, a white cell (WBC) and a differential white cell count. The RBC and WBC counts indicate the total number of red and white cells, respectively, per unit volume of blood. The differential white cell count indicates the relative number of the different types of white cells which make up the white cell count.
At present this most complex portion of blood analysis is performed manually using conventional microscopes to examine and count the cells of each specimen. A hematology technician performing a differential blood count identifies and counts cells and notes the presence of abnormal cells. When abnormal (usually immature) cells are present as indicated by the technician, the specimen is examined by a pathologist or hematoligist who attempts to arrive at a diagnosis of the disease that caused the appearance of the abnormal cells. This detailed examination is time consuming and based mainly on subjective impressions.
The length of time required to train a technician to perform differential blood counts with reasonable proficiency is on the order of several weeks. The technician counts and identifies a large number of cells. These are identified by comparison with a set of loosely defined "standards" --requiring subjective judgments which inherently lead to differences in cell counts between technicians. Typically, 5 to 10 minutes are required for a differential count. A technician can perform approximately 30 differential counts per day. Continuous peering into a microscope and counting cells quite often leads to weariness and carelessness which results in incorrect counts. The differential count is probably the longest and most difficult routine task still being performed by technicians in the clinical laboratory.
The frequency of performance of this type of diagnostic test has increased more than 100% in the last ten years. It is estimated that more than 200,000 differential blood counts are performed daily in the United States. The number of red and white blood cells counts performed on a daily basis is much higher than this. Although the cost of each test is relatively small, the large number of tests performed make them a major item in the operation of the clinical laboratory.
The factors outlined above clearly indicate a strong need for automation of the analysis of formed elements of blood by an instrument system that not only accomplishes tests more efficiently than manual methods, but also measures important parameters directly with high precision and reliability. The latter consideration is of crucial importance in upgrading the clinical usefulness of the tests and in providing quantitative diagnostic parameters that are not currently available.